Technical Field
The present disclosure relates to an apparatus and to a method for nucleic acid sequencing based on nanochannels.
Description of the Related Art
Given the ever-increasing importance that nucleic acid sequencing is assuming, various techniques have been developed for determining the nucleotide sequence.
Some of the known techniques are based upon the division of a nucleic acid molecule into short fragments, in general of some hundreds of bases, which are sequenced individually. The information collected on the individual portions is subsequently processed and aggregated for reconstructing the entire sequence of the bases that form the nucleic acid molecule. Reconstruction of the sequence is, however, an operation that is extremely complex and consuming in terms of resources, in particular, processing capacity, and time. Furthermore, it may happen that some fragments are not read and reconstructed correctly, and thus sequencing may be incomplete.
The developments in the nanotechnology sector have enabled development of new devices and techniques that enable handling of individual molecules, by exploiting, in particular, the electrical charge with which the nucleic acids are provided. For instance, in some devices appropriate electrical fields are used to cause passage of a single nucleic acid molecule through a nanopore in a membrane. In practice, the device has two chambers separated by a membrane, which has a nanopore and is provided with electrodes that enable creation of an electrical field. A solution containing molecules of a nucleic acid is loaded into one of the two chambers. Then, one end of a nucleic acid molecule, which normally presents as an entangled strand, may be introduced into the nanopore thanks to the electrical field. The dimensions of the nanopore are such that the presence of a portion of one molecule inhibits entry of ends of further molecules (the diameter of the nanopore may, for example, be between 5 nm and 10 nm). In this way, it is possible to isolate and handle a single sequence. The force exerted by the electrical field causes the strand forming the molecule to extend as it passes through the nanopore following after the end. The strand thus extended may be analyzed for sequencing.
Examples of devices of this type are described in Liu Q., Wu H., Wu L., Xie X., Kong J., et al. (2012), “Voltage-Driven Translocation of DNA through a High Throughput Conical Solid-State Nanopore”, PLoS ONE 7(9): e46014; DOI:10.1371/journal.pone.0046014; and in Tsutsui, M. et al., “Transverse Electric Field Dragging of DNA in a Nanochannel” Sci. Rep. 2, 394; DOI:10.1038/srep00394 (2012).
A limitation linked to the known devices lies in the low flexibility in controlling sliding of the strand through the nanopore and the forces exerted thereon. Since the accuracy in identifying the correct sequence of the bases depends markedly also upon these parameters, it is evident that fine control is decisive to obtain reliable results and efficient procedures of analysis.